Flat media, such as silicon or other semiconductor wafers, substrates, photomasks, flat panel displays, data disks, and similar articles require extremely low contamination levels. Even minute contaminants can cause defects. Accordingly, it is necessary to maintain a high level of cleanliness during all or nearly all stages of production of these types of flat media. The flat media described may be referred to below as “wafers”, although it will be understood that “wafers” means any form of flat media.
Wafers are typically processed in batches. For example, in manufacturing semiconductor chips, for use in computers, telephones, televisions, and other electronic products, silicon wafers will undergo many batch processing steps, such as oxidation, photolithography, diffusion, chemical vapor deposition, metallization and etching. Batch handling may occur throughout the entire production process, or for one or more processing steps or related handling operations. Batch processing of this type almost always utilizes some type of carrier or container to hold the wafers being processed.
A wafer carrier or container holds a group of wafers. The wafer carriers can be of various designs, and may be more specifically referred to as a wafer boat. In many applications, they are made of a suitable polymeric material, e.g., polypropylene or TEFLON® fluoropolymer. The sides and sometimes the bottom of the wafer boat have receiving slots formed to receive and hold the wafers in a spaced array with the faces of the wafers adjacent to one another. Typically, the central axes of the wafers are aligned. The wafers are slid into the carrier or container, such as from the side or above, and are removed by sliding them outwardly. The receiving slots are shallow so that the wafer is engaged only at the peripheral edges and along a thin marginal band extending inwardly from the periphery.
Wafer carriers can also be provided in the form of a protective case or box in which the wafers are held and are sealed against contamination during travel within the processing facility. Wafer carriers of this type are frequently designed to hold a wafer boat having a complementary design. The complementary relationship of the protective wafer carrier box and the wafer carrier boat allow the boat and supported wafers to be fully enclosed and securely held in place during transport. The term “carrier” referred to below means a carrier, a container, with or without a lid, or a wafer boat.
At certain stages in the manufacturing process, the wafer carriers must be cleaned. Cleaning them is difficult because they typically have features which include slots, grooves or apertures, and inside corners which can trap contaminants. The difficulty in cleaning is enhanced by the extremely low contamination levels which are required for processing the wafers.
Accordingly, cleaning of wafer carriers remains a difficult, time consuming and relatively costly procedure. Sticky-back labels, fingerprints, dust, metal particles, photoresist and organic chemicals may also contaminate the wafer carriers.
Various machines have been made and used for cleaning wafer carriers. In these machines, the carriers are mounted on a rotor and spin within a chamber, while cleaning solutions are sprayed onto the carriers. The spinning movement minimizes process time and also helps in drying the carriers. In certain applications, a surfactant is introduced and mixed with de-ionized water, at a concentration of approximately 1:10,000. Used in this way, the surfactant acts as a wetting agent which helps to remove loosely adhered particles. Typically the surfactant is used only once and then discarded as waste.
The surfactant is typically held in a vessel from which it must be transferred into the wafer carriers during the cleaning process. Since the surfactant stream is applied in such a small flow volume so as to produce the desired small concentration level, it is difficult to control volume flow of the surfactant into the carriers. In one system as described in U.S. patent application Ser. No. 09/113,440, surfactant is pumped from the bulk storage vessel into a holding tank where it is diluted to a desired level. The diluted surfactant solution is then drawn out of the holding tank by a venturi into the water stream where it is mixed or aspirated with the water. The water and surfactant mixture is then directed to the rinsing manifold ready for injection into the wafer carrier.
Accordingly, it is an object of the invention to provide an improved machine for cleaning carriers and containers for flat media.